I can recall a couple of years ago reading a blog (a pirate/ninja salvager from memory but the name escapes) who showed a screenshot of his pilot finishing all of the skills to V in the navigation tree.
It's a great achievement to complete all skills to V in a tree, some are going to take a very long time (and a lot of ISK) whereas others don't need completion to V (i.e. they only lower capacitor usage).
One of those trees that does deserve the effort is Navigation and it is with great pleasure I awoke this morning to see High Speed Maneauving V completed on my null sec pilot:
There is one skill missing but I don't use Micro Jump Drives (at this time) so as far as I'm concerned the tree is complete. The Jump skills were the longest and most painful but, consequently, the most rewarding to complete.
The character moves on to Int/Mem skills before finally starting on Gunnery, 4 years overdue I'd say. All he has is Gunnery III in that branch but when he's finished it's going to be Level V's all over the place!